The development of high-brightness solid state light sources has led to use of such devices in various lighting fixtures. Typically, a solid state light source is a direct current (DC) device, and so a driver circuit (also referred to simply as a “driver” or “power supply”) is typically required to operate the solid state light source on alternating current (AC) power (e.g., mainline 120V/60 Hz input AC power, or input from a typical dimmer switch). The driver typically converts an AC input to a stable DC voltage through use of a rectifier and a switching converter.
A number of switching converter configurations are well-known in the art, such as buck converters, boost converters, buck-boost converters, and the like, which are generally categorized as switching regulators. These devices include a switch, e.g. a transistor, which is selectively operated to allow energy to be stored in an energy storage device, e.g. an inductor, and then transferred to one or more filter capacitors. The filter capacitor(s) provide a relatively smooth DC output voltage to the load and provide essentially continuous energy to the load between energy storage cycles.
Another known type of switching converter includes a known transformer-based switching regulator, such as a “flyback” converter. In a transformer-based switching regulator, the primary side of the transformer is typically coupled to the output of the rectifier. A regulated DC output voltage is provided at the secondary side of the transformer, which is electrically isolated from the primary side of the transformer.
Further, to provide improved power factor, some driver circuits include a power factor correction circuit that may, for example, control operation of the switch in a switching converter. A power factor correction circuit typically monitors the rectified AC voltage, the current drawn by the load, and the output voltage to the load, and provides an output control signal to switch current to the load having a waveform that substantially matches and is in phase with the rectified AC voltage.